The invention relates to a process for transvinylation of a reactant carboxylic acid with a reactant vinyl ester to afford a product vinyl ester and the corresponding acid of the reactant vinyl ester in the presence of one or more ruthenium catalysts.
Transvinylation of carboxylic acids is used for preparing vinyl esters. This is to be understood as meaning the transfer of a vinyl unit from a reactant vinyl ester (1V) to a reactant carboxylic acid (2S) to generate a product vinyl ester (2V) and the corresponding acid of the reactant vinyl ester (1S).

EP 376075 B1 discloses the transvinylation of vinyl esters with carboxylic acids in the presence of palladium catalyst, wherein copper bromide and special lithium compounds are employed as cocatalysts.
In addition to palladium catalyst and mercury catalysts, the prior art also employs ruthenium compounds as catalyst for transvinylation of vinyl esters with carboxylic acids. Ruthenium compounds are notable for their high solubility, low volatility and high thermal stability. This is coupled with a high, temperature-inducible activity.
EP 351603 A2 (=EP 506070, U.S. Pat. Nos. 4,981,973, 5,155,253) describes a process for transvinylation of carboxylic acids using various Ru compounds as catalysts. The authors postulate a [Ru(CO)2RCO2] unit as the decisive structural element in the formation of the active species. Accordingly, all Ru compounds which may be converted into this structural element in situ may be employed as catalysts. Cited as a suitable starting species is, inter alia, the industrially available trinuclear Ru complex [Ru3O(OAc)6(H2O)3]OAc and it is found that this carbonyl-free ruthenium carboxylate is also converted into the active catalyst species in a nitrogen atmosphere instead of a carbon monoxide atmosphere. This complex is employed as catalyst in the transvinylation of various carboxylic acids in examples 2, 5, 6 and 14. While the reaction in examples 2, 5 and 6 takes place in a carbon monoxide atmosphere and with reaction times of 3 or 4.5 hours, the transvinylation in example 14 is effected at 100° C. in a nitrogen atmosphere. The significantly longer reaction time of 19 hours is attributable to a retarded formation of the active catalyst species in the absence of carbon monoxide. The use of [Ru3O(OAc)6(H2O)3]OAc in a continuous process is not described
Adv. Synth. Catal. 2013, 355, 2845-2859 confirms the theory from EP 351603 A2 and postulates a [Ru(CO)3(RCO2)2] complex as active catalyst species. In this case the catalytically active species is formed on the basis of RuCl3. Ru carbonyl propionate and Ru carbonyl valerate are produced by reaction of RuCl3with propionic acid or valeric acid. Carbonyl-free ruthenium carboxylates are not employed.
EP 497340 A2 (U.S. Pat. No. 5,210,207) describes a transvinylation process for preparing product vinyl esters having a higher boiling point than that of the reactant vinyl ester. Reactive distillation of at least one of the product components shifts the equilibrium of the reaction to the product side. It is preferable when the Ru catalysts described in EP 351603 A2 are used therefor. Example 8 employs [Ru3O(OAc)6(H2O)3]OAc as catalyst, it being pointed out that the conversion is retarded compared to a Ru carbonyl carboxylate. This suggests that the conversion of the employed [Ru3O(OAc)6(H2O)3]OAc into the active catalyst species is effected only slowly under the reaction conditions of example 8.
WO 92/09554 A1 describes a process where after the transvinylation the reaction mass is first separated and the product vinyl ester is then removed by azeotropic distillation. This process is aimed especially at separation of acid/vinyl ester mixtures having small differences in boiling point. The transvinylation reaction preferably employs Ru catalysts from EP 351603 A2. The examples do not describe the use of carbonyl-free ruthenium carboxylates as catalyst.
WO 2013/117294 A1 describes a continuous process for preparing vinyl carboxylate esters. The transition metal-catalyzed transvinylation is operated in a steady-state and the reaction mixture fractionated in a subsequent step. WO 2013/117295 describes a further implementation of this process comprising a subsequent derivatization of the conjugate acid of the reactant vinyl ester that is formed. The examples in both specifications employ predominantly Pd catalysts for the transvinylation. Two examples employ the Ru catalyst ruthenium dicarbonyl acetate. Carbonyl-free ruthenium carboxylate catalysts are not described.
The use of Ru catalysts in the transvinylation reaction entails clear advantages compared to Pd catalysts in terms of solubility, volatility, thermal stability and thermally inducible activity. Numerous Ru compounds can be converted into active Ru species in situ. On account of their large industrial scale availability, ruthenium(III) chloride and the trinuclear carbonyl-free Ru acetate complex [Ru3O(OAc)6(H2O)n(AcOH)3−n]OAc where n=0 to 3 or its (solvent-free) analog [Ru3O(OAc)6]OAc especially are advantageous. While the first-mentioned of these must first be formed by addition of a base, the Ru acetate complex of the prior art requires a carbon monoxide atmosphere in order to be converted into the active species within short reaction times. However, the avoidance of a carbon monoxide supply is highly desirable for reasons of safety engineering. A process in which a commercially available catalyst is converted into the active species without addition of carbon monoxide within short reaction times and which is thus suitable for use in continuous transvinylation processes has not hitherto been disclosed.